The influence of two indole inhibitors on the hydrolysis reaction of l-dipalmitoylphosphatidylcholine (l-DPPC) catalyzed by phospholipase A 2 (PLA 2 ) has been studied in the coexistence region using surface pressure as function of time (π–t) and Brewster angle microscopy (BAM) measurements. Similar experiments have been performed with l-DPPC vesicles made by ultrasonication method using transmission electron microscopy (TEM). Comparing the π–t curves and BAM images, which show defected domains after a certain reaction time, as well as TEM images of defected vesicles, one can conclude that the two indole inhibitors have different abilities in reducing the activity of PLA 2 . The described experiments show that BAM and TEM can be successfully used to study the influence of newly designed inhibitors on the hydrolysis reaction catalyzed by PLA 2 .